We wish to understand the basic biochemical mechanisms that serve to control the number and distribution of molecules on the surface of cells. Two cell surface molecules where number and distribution are highly regulated both in vivo and in vitro are the acetylcholine receptor (ACHR) and the acetylcholine esterase (ACHE). We have been studying them becaue good tools alreadh have been developed for their study and they are essential components of the neuromuscular junction; their study promises a greater understanding of both the cell surface and cholinergic synapses. Our studies with the monovalent and divalent ionophores have shown that 1. the release of acetylcholinesterase from cultured muscle cells can be completely blocked by very low concentrations of the monovalent ionophores, and 2. the divalent ionophores appear to suppress the production of both acetylcholinesterase and the acetylcholine receptor. We plan to decipher the mechanism by which acetylcholinesterase is released from cultured muscle and to test our hypothesis that intracellular free calcium controls the synthesis of th acetylcholinesterase and the acetylcholine receptor and perhaps other surface molecules found on muscle cells.